1. Field of the Invention
The present invention relates to a driving apparatus used for an image forming apparatus such as a printer, a facsimile machine, and a multifunction peripheral, and to an image forming apparatus using the driving apparatus.
2. Description of the Related Art
In recent years, many color image forming apparatuses have employed an intermediate transfer method, by which a toner image on a photosensitive body undergoes primary transfer onto an intermediate transfer body such as an intermediate transfer drum or an intermediate transfer belt in a primary transfer unit, and then the toner image of four colors on this intermediate transfer body undergoes secondary transfer onto a sheet member in a secondary transfer unit. The image forming apparatus using the intermediate transfer body is highly versatile and advantageous since various kinds of sheet members can be used such as thin paper, thick paper, postcards, and envelopes.
When a sheet member with a certain thickness or more enters the secondary transfer unit, however, there is caused a defect in that the speed of the intermediate transfer body which has been driven at a constant speed changes for a short period of time so that an image is transferred with a distortion in the primary transfer unit.
Further, there is an apparatus which simultaneously performs transfer and fixation of an image onto a sheet member since the secondary transfer unit and a fixation unit have become closer to each other in accordance with the downsizing of color image forming apparatuses. In this apparatus also, when a sheet member with a certain thickness or more enters the fixation unit, there is caused a problem in that the speed of a fixation roller or a fixation belt which have been driven at a constant speed changes for a short period of time, and thus an image is transferred with a distortion in the secondary transfer unit.
These defects can be avoided by estimating a timing when the speed change will be generated in the intermediate transfer body or the like before the sheet member enters the secondary transfer unit or the fixation unit and increasing the speed of the intermediate transfer body or the like when the sheet member enters the secondary transfer unit or the fixation unit to cancel out the speed change, which is called feed-forward control (see Patent Documents 1, 2, and the like). The timing when the speed change is generated can be estimated by using a sheet member sensor provided right before the fixation unit, as in an image forming apparatus disclosed in, for example, Patent Document 3. That is, the time from when the sheet member sensor senses the sheet member to when the sheet member enters the fixation unit is measured in advance. With the sensing of the sheet member as a start point, at a timing after the measured time has passed, the estimated speed change is generated.
[Patent Document 1] Japanese Patent Application Publication No. 2003-215870
[Patent Document 2] Japanese Patent Application Publication No. 2005-107118
[Patent Document 3] Japanese Patent Application Publication No. 2004-54120
FIGS. 15A and 15B are schematic diagrams showing the feed-forward control. A speed change Va can be expressed by a waveform of a velocity component in a predetermined period as shown in FIG. 15A. For example, as the feed-forward control of the case when the speed change Va is generated in the intermediate transfer body, the intermediate transfer body is controlled to be driven at a speed Vb which cancels out the speed change Va. As a result, the speed change Va can be canceled out and the intermediate transfer body can be driven at a constant speed as shown in FIG. 15B.
Here, when the speed change Va is generated for 100 ms and the speed of the intermediate transfer body is controlled by 1 ms increments to cancel out the speed change Va, 100 pieces of speed data to cancel out the speed change Va are required to be recorded in a recording unit. Further, more pieces of data are required to be recorded to cancel out plural different speed changes. Therefore, the recording unit is required to have a large recording area. Moreover, when the feed-forward control is performed, the data are required to be read per 1 ms from the recording unit by an operation unit for 100 ms when the speed change is generated, and the read data are required to be outputted to a driving control unit which controls driving of the intermediate transfer body. Since the operation unit is highly loaded, an operation processing property may be decreased and the appropriate feed-forward control may not be performed.
To solve this problem, a recording unit with a large recording area or a high performance operation unit which can sustain a high work load may be provided. However, there are resulting problems such as increase in manufacturing cost.